Apparently a common fix for spinning captains is to put on longer cranks since the long cranks reduce rpms for a given amount of pedal travel. I went from 170's to 175's (on my single bike) and dropped from spinning 110+ rpm to about 80 rpms. I worked hard to bring back some of that pedal speed and now ride at perhaps 100 rpm comfortably. If you ride shorter cranks more regularly (i.e. you ride the single bike more) then moving to 175's should cause you to slow down just a touch.
I'm close to TandemGeeks height and leg length and all normal rules would say 175's are too long. However I've not only ridden but also raced 175's successfully for about 5 years without any problems.
For cranks with square taper BB, check out some of the online shops that link up to QBP (Quality Bicycle Products). There are relatively cheap Sugino cranks listed - approx retail is $34 for the left and $20 for the right crank. I only know of one (bikeman.com) but I'm sure there are others. Any LBS would be able to order the same cranks through QBP.
hope this helps,
cdr